[PATCH] [libcxx] Require LLVM in libc++'s CMake.

[Jonathan Roelofs]

================
Comment at: test/lit.site.cfg.in:10
@@ -9,3 +9,3 @@
 config.enable_shared            = "@LIBCXX_ENABLE_SHARED@"
-config.enable_32bit             = "@LIBCXX_BUILD_32_BITS@"
+config.enable_32bit             = "@LLVM_BUILD_32_BITS@"
 config.enable_global_filesystem_namespace = "@LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE@"
----------------
EricWF wrote:
> jroelofs wrote:
> > `LLVM_BUILD_32_BITS` is a property of the host
> > `config.enable_32bit` is a property of the target
> > 
> > we should keep these separate, and not conflate host & target.... they're not always the same!
> I agree but I'm not sure the best way to handle this. compiler-rt and libcxxabi both already use LLVM_ENABLE_32BITS and they are libraries intended for the target. Do you have a suggestion about how to handle this?
Maybe we ought to detect the case when target == host, and use LLVM_ENABLE_32BITS as the default in that case, otherwise force the user to specify it (they're cross compiling anyway, so it doesn't hurt them to specify more things).

To do that, I'd keep the name `LIBCXX_BUILD_32_BITS`, and put the detection stuff in some CMake goop. Then fix libcxxabi to match libcxx. Compiler_rt, too.

http://reviews.llvm.org/D10055

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